I believe type IV hydraulic fluid's flash point is around 3-400 degrees F, RAT 5. I also think grease is in such limited quantities (bearings/joints) to preclude it being the cause of a serious fire - tires are more likely suspects in comparison.
There have been minute hydraulic leaks with a very fine spray. Put the 2 together and you might get a fire that will extinguish with airflow and then perhaps re-ignite.
Quite true. Gives even better reason for leaving the gear down, yes?
There have been problems with wiring insulation breaking down and sparking. There have been minute hydraulic leaks with a very fine spray.
MD-80 AUX HYD pump wiring comes to mind!